Hydrocarbons are often produced from well bores by sucker rod pumps, which are reciprocating pumps driven from the surface by drive units that move a polished rod up and down through a packing gland at a wellhead. Typically, a walking beam is pivotally mounted with one end of the beam being attached to the rod and with the beam being reciprocated by a drive unit. The drive unit consists of a prime mover connected to a reduction unit that drives a crank to reciprocate the walking beam.
While sucker rod pumps are relatively simple units, they are expensive to provide and maintain. Repair may require lifting of the entire down-hole unit to the surface. It is not unusual to have a mile or more of sucker rods or tubing that must be lifted and disassembled by one or two twenty five or thirty foot long sections at a time. This repair is costly in terms of repair labor and parts cost, and in the terms of lost revenue from the well.
Power requirements of the sucker rod pump are also significant, and are affected by the efficiency at which the unit is operating.
Sucker rod pumping units are typically designed to pump slightly more than the well can produce. Consequently, they eventually run out of liquids to pump, and draw gas into the cylinders, a condition known as a pump off condition.
In a pump off condition, the fluid level in the well is not sufficient to completely fill the pump barrel on the upstroke. On the next downstroke the plunger will impact the fluid in the incompletely filled barrel and send damaging shock waves through the components of the pumping system.
To minimize running pumped off, sucker rod pumps are generally operated with some type of controller. These controllers are either simple controllers designed not to detect a pump off condition, but rather to avoid an estimated pump off condition, or are more sophisticated pump off controllers designed to detect when a well pumps off and to shut the well down.
An example of these simple controllers are clock timers that start and stop the pumping unit in response to a set program designed to avoid a pump off condition. Unfortunately, these simple clock timers are not responsive to changing conditions, such as changes in the reservoir, or the occurrence of abnormal operating conditions. Such a changing condition may occur, with the timer continuing its on/off cycle until human intervention. Numerous methods have therefore been proposed to monitor and control sucker rod pump operation.
Common commercially available controllers monitor work performed, or something that relates to work performed, as a function of polished rod position. This information is generally presented in the form of a plot of load vs. rod string displacement on the rod string. For a normally operating pump, the shape of this plot (known as a “surface card”), is generally an irregular football shape. The area inside of this rectangle is proportional to the work being performed. Many pump off controllers utilize a plot such as this to determine when the sucker rod pump is pumped off, and then shutdown the pump for a time period when a criteria indicating the pump is not filling.
Other pump off controllers attempt to obtain load measurements that more accurately reflect the load on the sucker rod underground. For example, U.S. Pat. No. 3,306,210 discloses a pump off controller that monitors the load on the polished rod at a set position in the downstroke. Pump off is detected when the load exceeds a preset level at that set position. A disadvantage of this approach is that long cables are required from the sensor on the polished rod to the controller. These cables hang around interfering with the most frequent maintenance activities in the well, being continually damaged by service crews. Additionally since they are subject to the repetitious motion of the well are prone to failure. Also, a separate position sensor is typically used on the walking beam, further complicating design.
In use, monitoring and recalibration of pump off controllers may be required on a regular basis to ensure that wear, drift, loss of sensitivity, temperature effects, and a myriad of other conditions do not render the detection of pump off conditions ineffective over time. Monitoring and servicing wells is expensive and time-consuming and requires the operator to physically stand by the pump off controller to gather and analyze operating data provided by conventional numerical or graphic displays, which is time-consuming and inefficient.
For at least the foregoing reasons, there remains a need for an apparatus that is easily installed and operated with the minimum of calibration or operator intervention, for a method that can automatically identify and implement the optimum time out for the well, and provides features for remote data collection and remote operation.